Courtship performance as function of body condition in an ‘ancient’ form of sperm transfer: supplementary material

In most animal species, body condition has a fundamental role in fitness. In males, sexual selection generally favors larger body size or greater weight. This may result in males with better condition performing more vigorous courtships, and biasing female preferences. The effects of body condition on mating performance have been extensively studied in different animal groups. Among arachnids, scorpions are an interesting group for evaluating the effects of these sexual traits on mating performance, since they exhibit an ancient mode of indirect sperm transfer. Scorpion males deposit a single spermatophore on the soil to transfer the sperm to the females, and therefore, the production of spermatophores involves a high cost for them. In this study, we use the scorpion Bothriurus bonariensis as a model to evaluate different patterns of sexual behavior as a function of the body condition of both males and females. We found that males with a better body condition performed the mating dance stage more quickly than males with a lower condition. In addition, males performed the sexual sting behavior for a longer time with females in a better condition. Our results suggest that a better condition provides a mating advantage to males and represents an indicator of courtship performance. Given that female quality is usually correlated with fecundity, males mating with females with a better body condition probably have higher reproductive success.

在多数动物物种中，身体状况对其适合度（fitness）具有根本性的影响。对于雄性个体而言，性选择通常更青睐体型更大、体重更高的个体。这将使得身体状况更佳的雄性展现出更具活力的求偶行为，并影响雌性的择偶偏好。
身体状况对交配表现的影响已在不同动物类群中得到广泛研究。在蛛形纲动物（arachnids）中，蝎子是探究此类性征对交配表现影响的理想类群，因其演化出了古老的间接精子传递方式。蝎子雄性会在土壤表面沉积单个精荚（spermatophore）以完成向雌性的精子传递，因此精荚的生产对雄性而言代价高昂。
本研究以阿根廷双尾蝎（Bothriurus bonariensis）为实验模型，基于雌雄个体的身体状况，探究其性行为的不同表现模式。研究结果显示，身体状况更佳的雄性完成交配舞阶段的速度快于身体状况较差的雄性。此外，当与身体状况更佳的雌性交配时，雄性的性刺行为持续时间更长。
本研究结果表明，更佳的身体状况能够为雄性带来交配优势，同时可作为求偶表现的可靠衡量指标。鉴于雌性质量通常与其繁殖力（fecundity）呈正相关，与身体状况更佳的雌性交配的雄性，其繁殖成功率大概率更高。